Among the most important physical characteristics of plasticized polyvinyl chloride (PVC) are flexibility and pliability. These physical characteristics are achieved by compounding PVC resin with one or more materials which serve as plasticizers following their addition to the PVC resin. Plasticizers are high boiling point liquids that do not evaporate from the matrices they are added to, but rather preserve the flexibility of plastic sheeting and film. The majority of PVC plasticizers currently utilized in industrial processes are petroleum-derived phthalates and benzoate compounds. Dioctyl phthalate (DOP) and diallyl phthalate (DAP) are examples of petroleum-derived compounds commonly used as primary plasticizers for PVC.
While effective as primary plasticizers, petroleum-derived plasticizers are subject to several significant limitations. In addition to being derived from a nonrenewable source, petroleum-derived PVC plasticizers are often expensive to produce due to fluctuations in the price and availability of crude oil. Furthermore, petroleum-derived plasticizers such as DOP are suspected to disrupt human endocrine activity (see Modern Plastics, January 1998, p 35).
Epoxidized soybean oil (ESO) can be added to a PVC formulation as a stabilizer. ESO is generally recognized as safe and is therefore of particular value in plastics formulations intended for medical and food applications as well as toys. Epoxidized linseed oil is also used commercially, although less commonly due to its higher cost. Although some epoxidized vegetable oils are commercially available as plasticizers, ESO has limited compatibility with PVC at levels above 10 parts per hundred resin (phr).
Drying oils are organic liquids which, when applied as a thin film, readily absorb oxygen from the air and polymerize to form a relatively tough, elastic film. Drying oils are usually natural products from renewable resources such as linseed oil, tung oil, soybean oil, tall oil, dehydrated castor oil, and the like which are included as combinations of such natural oils or their fatty acids in various synthetic resins. The drying ability is due to the presence of unsaturated fatty acids, especially linoleic and linolenic, frequently in the form of glycerides but also as their corresponding carboxylic acids.
Printing inks utilize a vehicle as a carrier for the pigment. The vehicle is required to wet the pigment by displacing air at the pigment surface, it is also responsible for getting the pigment to the substrate and holding it there, as well as contributing greatly to the final gloss, setting and various other properties in the ink film. Traditionally, such vehicles have been made from solvents, vegetable oils, resins (both liquid and hard) and may include other components such as co-solvents, rheological modifiers, driers and anti-oxidants. The most commonly utilized vehicle for paste printing inks has been based upon petroleum distillates as the major solvent. Inks containing petroleum distillates as a solvent contain a non-renewable resource and emit organic vapors during the handling and drying processes.